This invention relates in general to a combined power supply and control circuit for a heavy vehicle antilock brake system (ABS). More specifically, using line carrier communication technology, the present invention electronically communicates between local wheel mounted electronic control modules and a central electronic control unit through existing power lines.
Electronic antilock braking systems (ABS) for heavy vehicles, such as tractor trailer rigs, are well known in the art. ABS was designed to help the driver maintain steering and avoid skidding during emergency braking. The goal of an ABS is to keep the wheels turning in an emergency stop. Friction between the tread of the tire and the road surface during braking is at its maximum just before the wheel locks up. It is therefore beneficial to keep the wheels rotating at a rate of about 80% of the free rolling velocity for the vehicle""s speed. The distance the vehicle will skid with locked up wheels is much greater than if the wheels were kept rotating at a point just before they lock up.
ABS works by limiting the braking pressure to any wheel which starts to lock up. This allows maximum braking force to be applied without brake lockup which would cause skidding. If standard non-ABS brakes are applied too hard, the wheels lock or skid, and the driver loses the ability to steer. If steering is lost, the vehicle skids in a straight line. ABS allows the driver to continue steering during hard braking in an emergency stop, thereby allowing the driver to maintain control of the vehicle.
To prevent skidding with standard non-ABS brakes, drivers had to either pump the brakes or sense the lockup and release the brake entirely. If only one wheel lost traction and started to skid, the driver would have to reduce braking force on all wheels to prevent a skid. On the other hand, ABS equipped vehicles maintain optimum braking force on each individual wheel. Thus, the braking force applied to the wheels with good traction can be maximized even if other wheels lose traction. As long as the wheels keep their grip on the road, the driver is able to steer and brake each wheel to its maximum capacity.
Antilock brake systems generally use a central electronic control module (ECM) to monitor and control the braking system. Individual wheel speed sensors communicate with the central ECM to determine if one or more wheels are about to lock up during braking. The system can electronically sense that one or more wheels are rotating at a different speed than the others on the vehicle. If rapid wheel speed deceleration indicative of lockup is detected during braking, the ECM signals to limit or reduce the braking pressure on that wheel. It then causes the braking action, on the wheel spinning more slowly due to lost traction, to be momentarily reduced, and braking action to that wheel is pulsed so the ECM can try to determine how much traction is available and, in turn, how much braking action that wheel should be given. This prevents skidding and allows the driver to maintain steering control. In addition, the ABS tests itself every time the vehicle is started and every time the brakes are applied. The system evaluates its own signals, and if a defect is detected the system then turns off leaving normal braking unaffected.
Current ABS systems for heavy duty vehicles, such as certain tractor trailer combinations, usually consist of up to two ECMs with up to eight wheel speed sensors and five antilock modulators. All of the control wiring required for these sensors and modulators must be routed from each device back to the cental ECM. As a result, the ABS control wiring for a full sized tractor trailer rig requires installation of hundreds of feet of control wiring. Control wiring must be routed from each individual wheel back to the central ECM, and this wiring is susceptible to failure due to vibration, short circuit, corrosion, wear, or ground failure.
The connection between a tractor and a trailer normally includes a wiring harness with multi-pin electrical connection plug plus connections for the air brake command and air brake supply lines. Electrical communication signals between the tractor and the trailer must pass through the wiring harness. The number of wires present in the existing wiring harness is limited to the number of pins in the multi-pin plug, and each of the existing pins already has a dedicated purpose. The limited number of available pins on an existing wiring harness make it difficult to expand the number of communication signals which can be sent between the tractor and the trailer, without resorting to extra trailer wiring and extra trailer plugs. Connection plugs are also susceptible to failure due to wear, vibration, or corrosion.
The additional quantity of vehicle wiring and connection plugs makes the system more complex, because each time the trailer is hitched up the operator must connect and check additional plugs. The system is also less reliable, because hundreds of feet of extra wire and extra plugs between the tractor and trailer create numerous potential failure points which may fail due to short circuit, ground failure, wear, vibration, or corrosion.
As a result, there is a need for an ABS which permits control signals to be transmitted and received between a central ECM and the wheels of tractor and trailer, without resorting to extra tractor and trailer wiring and plugs. In view of the above, it is an object of the invention to reduce the wiring harness requirements for a tractor/trailer ABS system.
The present invention provides a combined power supply and electronic control circuit using existing power supply wires to communicate ABS control signals between individual electronic control units, mounted at each wheel of a tractor and a trailer, and a central electronic control module. The central electronic control module communicates with the wheel mounted electronic control modules using low voltage hi-frequency AC carrier signals. Each wheel mounted electronic control unit is assigned a signature voltage and frequency, permitting simultaneous communications by all of the wheel mounted electronic control units with the central electronic control module.
In a preferred embodiment, the combined power supply and electronic control circuit for an antilock braking control system for a wheeled vehicle includes a central electronic control module having a power terminal and a grounding terminal, a main power bus connected to the power terminal, a main grounding bus connected to the grounding terminal, and a plurality of wheel mounted electronic control units, each electronic control unit including a power terminal connected to the main power bus and grounding terminal connected to the main grounding bus.
In operation, the central electronic control module communicates with the wheel mounted electronic control units via the main power bus and the main grounding bus using the AC carrier signals that are transmitted over the base DC voltage supplied by the main power bus. Accordingly, the requirement for additional wiring and plugs to connect the ECUs to the ECM is avoided, thereby greatly enhancing the reliability of the system while reducing the expense and complexity of the system.
Other advantages and features of the invention will become apparent from the following detailed description of the preferred embodiments and the accompanying drawings